Semiconductor Integrated Quantum Optical Circuits

Abstract

Applying the rules of quantum rather than classical physics makes big differences to how we can manipulate information. A classical 'bit' of data can have one of two values, '0' or '1'. Its quantum counterpart, the qubit, can be in a state which is a superposition of the two values, in the sense of having both values at the same time. This, along with entanglement (Einstein's 'spooky' action at a distance) could enable quantum computers to out-perform current computers by huge margins. However making such a machine is very difficult; it is challenging to control large quantum systems while simultaneously isolating them from their environment sufficiently well to be able to carry out a useful calculation. Currently, using a number of different sorts of hardware (trapped ions, atoms at nano-Kelvin temperatures, superconducting circuits, single photons in silicon waveguides), it is possible to perform some simple quantum algorithms on arrays of a few qubits. However, for all these systems, there are very significant challenges to scaling such demonstrators up into useful devices.

We propose to develop quantum circuits using a different technology, III-V semiconductor materials (GaAs, AlGaAs, InGaAs etc). Our circuits will employ photons and electron spins as qubits, making use of the optical properties of the III-V materials to carry out the quantum operations. A big advantage of the III-V semiconductors is that a mature photonics technology with advanced fabrication capabilities already exists, which will enable us to put all the elements of a circuit on a single microchip. With this level of integration, our approach is intrinsically scalable. Our five year vision is to construct circuits containing all the basic building blocks required to achieve quantum information processing: single photon sources to generate photon qubits, communication channels between qubits, quantum logic gates, memories consisting of spin qubits, and on-chip single photon detectors.

Circuits of this type could form the building blocks of future quantum computers, but they can also perform useful quantum functions outside the realm of large scale quantum computation. With this level of complexity, it is possible to build quantum repeaters that enable wide-scale secure quantum communication networking. There are also applications in quantum metrology, where the properties of quantum mechanics can be used to obtain precision beyond the fundamental limits imposed by classical physics. Potential areas that may benefit here are magnetic sensors and microscopy.

To pursue this vision of an integrated quantum technology, we will have to push forward the state of the art in semiconductor physics and device fabrication. On the physics side, our expected highlights include demonstrating full control of the nuclear spins in a device, obtaining entanglement of remote qubits on a chip, creating photon blockade structures, where the presence of a single photon prevents any more from entering, and developing control of light-matter interactions on the scale of single quanta. The targets on the technology side are equally challenging and will include tuning of quantum dot properties to achieve tightly controlled emission properties, the growth of dots in defined positions for incorporation in optical cavities, and highly reproducible lithography to achieve efficient circuit performance. All these topics will be central to our goals and will be addressed within the proposal; in addition they have potential to be of significance for a wide range of related nanoscale photonic technologies.

Planned Impact

The beneficiaries of our research will be in both academia and industry, in the UK, EU and worldwide. Enhancements to the capabilities of UK industry will lead further to benefits to the economy as a whole.

Our research is carried out in the highly technologically significant field of III-V semiconductors (e.g. for LEDs, lasers, high frequency transistors etc). Our new directions exploit quantum physics in nanoscale III-V structures and have potential to lead to a new generation of technologies for adoption by industry, for exploitation in the fields of quantum communication, cryptography, and computation and in precision measurement and sensors.

A series of workshops will be held in which our research will be showcased, with active industrial participation, making industry aware of long term opportunities which arise from the physics and technology outputs of our work. With participation of professional facilitators, activities devoted to blue-skies thinking and exploration of cross-disciplinary opportunities (creativity@home) will be held, to which industrial participants will be invited. We will use the opportunity of the industry-focussed III-V Road-mapping exercise being carried out over the next two years, and being led from Sheffield, to provide a further opportunity to achieve transfer of our results and ideas to an industrial forum.

Training of high quality personnel will be an important output of our Programme. Our research encompasses many of the key features of III-V technology, including crystal growth, device fabrication and advanced physics. Our PhD graduates are highly employable by industry. Based on our track record we expect to supply a minimum of seven PhD graduates into British industry and government laboratories over the lifetime of the grant. Specific programmes will be put in place to achieve effective training for future careers. These steps will include formal training in device fabrication and crystal growth in the advanced laboratories of the III-V Facility at Sheffield, training in device physics and simulation techniques and much practice in both oral and written presentations, further equipping graduates in advantageous ways for careers in industry and academia.

On a wider front, we will disseminate the fruits of our research to specific sections of the wider public: we will showcase our work at scientific exhibitions, write articles of popular scientific magazines, and carry out presentations of the most-attention catching parts of our research to sixth-form colleges.

On the academic side, we have highly successful track records of publication of our work in top quality international journals, including for example ten publications in the top-rated physics journal in the last year. We will place high priority on maintaining this level of dissemination in the Programme Grant, bringing much health to the physics discipline and benefiting academia in a very broad sense. Our training is also highly successful in supplying excellent researchers for careers in academia; more than ten individuals trained in our group now hold senior academic positions; a similar level of success is expected as a result of the Programme grant.

First Semiconductor Quantum Optical Circuits of relevance to future quantum technologies.Importance of self assembly for very long coherence times, the times during which a wave function maintains its phase.